Power supply device and arc machining power supply device

ABSTRACT

A power supply device that is applicable to both 200 V and 400 V series input power by switching the operation of an auxiliary switching circuit with a switching switch. When a relatively large output is requested, PWM control is performed to adjust the on pulse width of a control pulse signal provided to switching elements of an inverter circuit and an auxiliary switching circuit, which is operated in cooperation with the inverter circuit. When a relatively small output is requested, PSM control is performed to adjusting a phase difference of two control pulse signals provided to the same set of switching elements in the inverter circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2011-254099, filed on Nov. 21,2011, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a power supply device and an arcmachining power supply device that includes an inverter circuit, whichconverts alternating current (AC) power from a commercial power intodirect current (DC) voltage and then converts the DC voltage to apredetermined AC voltage, and are applicable to input power including aplurality of different voltage values.

Japanese Laid-Open Patent Publication No. 2009-17656 describes anexample of a power supply device for an arc machine or the like thatincludes a DC converter circuit, which converts AC voltage to DCvoltage, and an inverter circuit, which converts the DC voltage to ACvoltage. The DC converter circuit includes a rectifier circuit, whichrectifies commercial power (three phase AC power) and a smoothingcapacitor, which smoothes the rectified DC voltage. The inverter circuitincludes a bridge circuit of a plurality of switching elements (first tofourth switching elements). The inverter circuit synchronously controlsthe activation and deactivation of a predetermined combination of theswitching elements to convert the DC voltage from the DC convertercircuit into a predetermined high frequency AC voltage. Thepredetermined high frequency AC voltage from the inverter circuit isfurther converted into machining DC voltage that is suitable for arcmachining such as arc welding and arc cutting.

The power supply device includes a switching switch that switchesbetween an internal operation of a specification corresponding to acommercial power of 200 V (200 V series) and an internal operation of aspecification corresponding to a commercial power of 400 V (400 Vseries).

Specifically, an auxiliary switching circuit is arranged between the DCconverter circuit and the inverter circuit. The auxiliary switchingcircuit includes an auxiliary capacitor, which is connected between twopower lines at the upstream side of the inverter circuit. Further, theauxiliary switching circuit includes, between the DC converter circuitand the auxiliary switching circuit, fifth and sixth switching elements,which are arranged in the two power lines, and seventh and eighthswitching elements, which are connected in series between the two powerlines. The DC converter circuit includes a smoothing capacitor, namely,first and second smoothing capacitors connected in series between thetwo power lines in the present embodiment. The switching switch isconnected between a first node of the first and second smoothingcapacitors and a second node of the seventh and eighth switchingelements. The switching switch connects and disconnects the first nodeand the second node.

When the commercial power of 200 V is supplied (hereinafter referred toas the 200 V series input), the switching switch disconnects the firstnode and the second node and supplies the inverter circuit with thevoltage applied to the two ends of the first and second smoothingcapacitors that are connected in series. When the commercial power of400 V is supplied (hereinafter referred to as the 400 V series input),the switching switch connects the first node and the second node. As aresult, by activating and deactivating a predetermined combination ofthe fifth to eighth switching elements, the voltage applied to the twoends of the first smoothing capacitor and the voltage applied to theends of the second smoothing capacitor are alternately supplied to theinverter circuit. In this manner, the same DC voltage is supplied to theinverter circuit regardless of the voltage value of the input power.

In the auxiliary switching circuit, a soft switching control isperformed to deactivate predetermined ones of the fifth to eighthswitching elements before deactivation of the first to fourth switchingelements of the inverter circuit. This switches each element with a zerovoltage and zero current thereby reducing switching loss.

When controlling the inverter circuit, a typical pulse width modulationcontrol (PWM control) is performed to adjustment the output of the powersupply device to an extremely small level. In such a case, a controlpulse signal provided to the switching elements of the inverter circuitand the auxiliary switching circuit, which is operated in cooperationwith the inverter circuit, is set to have an extremely narrow on pulsewidth. This may hinder the activation of the switching elements and leadto shortcomings such as output instability and biased magnetism. It isthus desired that the output of the power supply device be stabilizedwhile using PWM control.

One aspect of the present invention is a power supply device including aDC converter, and inverter circuit, an auxiliary switching circuit, apulse width modulation circuit, a phase shift control unit, and acontrol switching unit.

The DC converter circuit includes a rectifier circuit and first andsecond smoothing capacitors, which are connected in series and arrangedbetween two power lines at an output side of the rectifier circuit. TheDC converter circuit rectifies and smoothes input AC power and convertsthe input AC power into DC voltage.

The inverter circuit includes a bridge circuit of first to fourthswitching elements. Predetermined sets of the first to fourth switchingelements are alternately activated and deactivated to convert the DCvoltage to a predetermined AC voltage.

The auxiliary switching circuit includes an auxiliary capacitor, whichis connected between the two power lines between the DC convertercircuit and the inverter circuit, fifth and sixth switching elementsrespectively arranged on the two power lines between the DC convertercircuit and the auxiliary capacitor, seventh and eighth switchingelements connected in series between the two power lines between theauxiliary capacitor and the first and sixth switching elements, and aswitching unit that connects or disconnects a first node of the firstand second smoothing capacitors and a second node of the seventh andeighth switching elements.

The switching unit disconnects the first and second nodes when the inputAC power has a first voltage value to supply a voltage across twoterminals of the first and second smoothing capacitors to the invertercircuit. The switching unit connects the first and second nodes when theinput AC power has a second voltage value that is two times greater thanthe first voltage value so that soft switching control is performed byactivating and deactivating predetermined sets of the fifth to eighthswitching elements, alternately supplying the inverter circuit with avoltage across the terminals of the first or second smoothing capacitor,and deactivating a predetermined one of the fifth to eighth switchingelements before the first to fourth switching elements are deactivatedto stop the voltage supplied to the inverter circuit.

The pulse width modulation control unit adjusts an on pulse width of acontrol pulse signal provided to the first to fourth switching elementsand adjusts an on pulse width of a control pulse signal provided to thefifth to eighth switching elements in accordance with the adjustedwidth.

The phase shift control unit adjusts a phase difference of two controlpulse signals provided to the same set of switching elements in thefirst to fourth switching elements or adjusts a phase difference of twocontrol pulse signals provided to predetermined ones of the first tofourth switching elements and corresponding ones of the fifth to eighthswitching elements.

The control switching unit operates the pulse width modulation controlunit when a relatively large output is requested and operates the phaseshift control unit when a relatively small output is requested.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an arc machining power supply deviceaccording to one embodiment;

FIG. 2 is a waveform chart of a control pulse signal taken during a PWMoperation (during a large output) for 400 V series inputs;

FIG. 3 is a waveform chart of a control pulse signal taken during aPWM-PSM critical operation (during a medium to small output) for 400 Vseries inputs;

FIG. 4 is a waveform chart of a control pulse signal taken during a PSMoperation (during an extremely small output) for 200 V series inputs;

FIG. 5 is a waveform chart of a control pulse signal taken during a PWMoperation (during a large output) for 200 V series inputs;

FIG. 6 is a waveform chart of a control pulse signal during a PWM-PSMcritical operation (during a medium to small output) in the 200 V seriesinput;

FIG. 7 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 200 V series inputs;

FIG. 8 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 400 V series inputs inanother example;

FIG. 9 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 200 V series inputs ofanother example;

FIG. 10 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 400 V series inputs inanother example;

FIG. 11 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 200 V series inputs inanother example;

FIG. 12 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 200 V series inputs inanother example;

FIG. 13 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 400 V series inputs inanother example;

FIG. 14 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 200 V series inputs inanother example; and

FIG. 15 is a waveform chart of a control pulse signal during a PSMoperation (during an extremely small output) for 200 V series inputs inanother example.

DETAILED DESCRIPTION OF THE INVENTION

An arc machining power supply device according to one embodiment of thepresent invention will now be described with reference to the drawings.

FIG. 1 shows an arc machine 10 including an arc machining power supplydevice 11 of the present embodiment. The arc machine 10 suppliesmachining DC voltage from the power supply device 11 to a torch TH sothat the torch TH generates an arc directed toward a machining subjectM. The arc machine 10 carries out arc machining such as arc welding, arccutting, and the like on the machining subject M. The arc machiningpower supply device 11 of the arc machine 10 includes a DC convertercircuit 12, which converts the supplied commercial power (three phase ACvoltage) into DC voltage, and an inverter circuit 13, which converts theDC voltage into a predetermined high frequency AC voltage. The arcmachining power supply device 11 also includes a transformer INT and asecondary side circuit to convert the high frequency AC voltage from theinverter circuit 13 into machining DC voltage.

The DC converter circuit 12 includes a primary side rectifier circuitDR1 and first and second smoothing capacitors C1 and C2. The primaryside rectifier circuit DR1, which includes a bridge circuit of sixdiodes, performs full-wave rectification on three-phase AC power. Thefirst and second smoothing capacitors C1 and C2 are connected in seriesbetween two power lines L1 and L2 to smooth the output voltage of therectifier circuit DR1. The DC converter circuit 12 generates DC voltagefrom the supplied AC power. The first and second smoothing capacitors C1and C2 have the same capacitance. A voltage detection circuit IV, whichdetects the DC voltage, is connected between the two power lines L1 andL2 in the DC converter circuit 12. The voltage detection circuit IVprovides an output control circuit SC (described later) with thedetected DC voltage as a voltage detection signal Iv. The output controlcircuit SC determines whether to supply the AC power of the 200 V seriesor the AC power of the 400 V series to the power supply device 11.

The inverter circuit 13 includes a bridge circuit of first to fourthswitching elements TR1 to TR4 connected to the two power lines L1 andL2. In the present embodiment, the first to fourth switching elementsTR1 to TR4 are insulated gate bipolar transistors (IGBTs). The first andthird switching elements TR1 and TR3 are connected in series between thetwo power lines L1 and L2. The second and fourth switching elements TR2and TR4 are connected in series between the two power lines L1 and L2. Aprimary side coil in the transformer INT includes one end connectedbetween the emitter of the switching element TR1 and the collector ofthe switching element TR3 and another end connected between the emitterof the switching element TR2 and the collector of the switching elementTR4. First to fourth diodes D1 to D4 are reversely connected to thefirst to fourth switching elements TR1 to TR4, respectively. Acombination of the first and fourth switching elements TR1 and TR4 and acombination of the second and third switching elements TR2 and TR3 arealternately activated and deactivated under the control of the outputcontrol circuit SC. This converts the DC voltage from the DC convertercircuit 12 into a predetermined high frequency AC voltage that issupplied to the primary side coil of the transformer INT.

An auxiliary switching circuit 14 and an auxiliary capacitor C3 arearranged between the inverter circuit 13 and the DC converter circuit12. The auxiliary switching circuit 14 includes fifth to eighthswitching elements TR5 to TR8 that are configured by four IGBTs. In thepresent embodiment, the fifth to eighth switching elements TR5 to TR8are IGBTs. The fifth switching element TR5 is arranged on the power lineL1 at the downstream side of the first and second smoothing capacitorsC1 and C2. The sixth switching element TR6 is arranged on the power lineL2 at the downstream side of the first and second smoothing capacitorsC1 and C2. The seventh and eighth switching elements TR7 and TR8 areconnected in series between the two power supplies L1 and L2 at thedownstream side of the fifth and sixth switching elements TR5 and TR6.Fifth to eighth diodes D5 to D8 are reversely connected to the fifth toeighth switching elements TR5 to TR8, respectively. The auxiliarycapacitor C3 is connected between the two power lines L1 and L2 at thedownstream side of the seventh and eighth switching elements TR7 andTR8.

A switching switch S1 is connected between a node N2 of the emitter ofthe seventh switching element TR7 and the collector of the eighthswitching element TR8 and a node N1 of the first and second smoothingcapacitors C1 and C2. In the present embodiment, the switching switch S1is a relay. The switching switch S1 is deactivated when determined thatthe AC power of 200 V series is supplied under the control of the outputcontrol circuit SC. This disconnects the two nodes N1 and N2. Theswitching switch S1 is activated when determined that the AC power of400 V series is supplied under the control of the output control circuitSC. This connects the two nodes N1 and N2. The fifth to eighth switchingelements TR5 to TR8 are activated and deactivated in synchronism withthe switching elements TR1 to TR4 under the control of the outputcontrol circuit SC. This reduces the switching loss of the first tofourth switching elements TR1 to TR4 in the inverter circuit 13. Theoutput control circuit SC performs a control corresponding to the 200 Vseries AC power and a control corresponding to the 400 V series AC poweron the fifth to eighth switching elements TR5 to TR8.

The transformer INT includes, at a secondary side, a full-waverectification secondary rectifier circuit DR2, which is configured bytwo diodes, and a DC reactor DCL. The DC reactor DCL is connected to thetorch TH by an output line L3. An intermediate point of the secondaryside coil of the transformer INT is connected by an output line L4 to amachining subject M. The transformer INT adjusts the value of the highfrequency AC voltage generated by the inverter circuit 13. The secondaryrectifier circuit DR2 and the DC reactor DCL convert the adjusted highfrequency AC voltage into an arc machining DC voltage. The torch THgenerates an arc directed toward the machining subject M based on thearc machining DC voltage that is supplied.

An output current detection circuit ID, which detects the actual outputcurrent value is connected to the output line L4. The output currentdetection circuit ID provides a comparison calculation circuit ER withthe detected output current value as an output current detection signalId. The comparison calculation circuit ER compares the output currentdetection signal Id with an output current set signal Ir from an outputcurrent setting unit IR. The output current setting unit IR is set withthe output current value by human operation and the like so as to becomethe output current value corresponding to the machining subject M onwhich to perform arc machining. The output current setting unit IRoutputs the set output current set signal Ir to the comparisoncalculation circuit ER. The comparison calculation circuit ER providesthe output control circuit SC with a comparison calculation signal Er,which indicates the comparison result of the output current detectionsignal Id and the output current set signal Ir. In this manner, thecomparison calculation circuit ER provides the output control circuit SCwith the comparison calculation signal Er, which indicates the deviationof the output current value and the set value. The output controlcircuit SC uses the comparison calculation signal Er to perform feedbackcontrol.

The output control circuit SC determines the DC voltage generated by theDC converter circuit 12 based on the voltage detection signal Iv fromthe voltage detection circuit IV. The output control circuit SCdetermines whether the 200 V series AC voltage or the 400 V series ACvoltage is supplied based on the detected DC voltage. The output controlcircuit SC activates the switching switch S1 when determining that a 400V series AC voltage has been supplied and deactivates the switchingswitch S1 when determining that a 200 V series AC voltage has beensupplied. The output control circuit SC controls the inverter circuit 13and the auxiliary switching circuit 14 as shown by the timing waveforms(control pulse signals) in FIGS. 2 to 4 and FIGS. 5 to 7. The switchingswitch 1 is activated to be applicable to a 400 V series AC power beforeAC power is supplied.

As described above, the output control circuit SC determines thedeviation of the output current value and the set value based on thecomparison calculation signal Er. The output control circuit SC sets theswitching control of the inverter circuit 13 to pulse width modulationcontrol (PWM control) when requesting a range from a large output to asmall output (hereinafter referred to as the large to small outputrequest) in view of the deviation. The output control circuit SC setsthe switching control of the inverter circuit 13 to phase shift control(PSM control) when requesting an extremely small output (hereinafterreferred to as the extremely small output request). The output controlcircuit SC synchronizes the switching control of the auxiliary switchingcircuit 14 with the control mode of the inverter circuit 13 so that theauxiliary switching circuit 14 operates in cooperation with the invertercircuit 13.

When a 400 V series voltage is supplied (hereinafter referred to as the400 V series input), the switching switch S1 is activated, and the nodeN1 of the first and second smoothing capacitors C1 and C2 and the nodeN2 of the seventh and eighth switching elements TR7 and TR8 areconnected. In this case, as shown by the timing waveform charts of FIGS.2 to 4, the output control circuit SC controls the first to eighthswitching elements TR1 to TR8 of the inverter circuit 13 and theauxiliary switching circuit 14 with a plurality of control pulsesignals.

Specifically, when performing the large to small output request, theoutput control circuit SC performs the PWM control using a plurality ofcontrol pulse signals, as shown in FIG. 2 and FIG. 3. The two controlpulse signals respectively provided to the first and fourth switchingelements TR1 and TR4 of the inverter circuit 13 simultaneously rise toan H level or fall to an L level. The two control pulse signals providedto the second and third switching elements TR2 and TR3 of the invertercircuit 13 also simultaneously rise to an H level or an L level. Thefour control pulse signals provided to the first to fourth switchingelements TR1 to TR4 are set so that a combination of the first andfourth switching elements TR1 and TR4 and a combination of the secondand third switching elements TR2 and TR3 are alternately activated anddeactivated. The output control circuit SC sets the control pulse signalwith a wide on pulse width Wm when requesting a large output and setsthe control pulse signal with a narrow on pulse width Wm as therequested voltage value decreases. That is, the on pulse width Wm isadjusted between a maximum width Wmx of FIG. 2 and a minimum width Wm0of FIG. 3 in accordance with the large to small output request.

The two control pulse signals provided to the fifth and eighth switchingelements TR5 and TR8 of the auxiliary switching circuit 14 rise togetherwith the two control pulse signals provided to the first and fourthswitching elements TR1 and TR4 and fall a predetermined time t1 beforethe two control pulse signals are provided to the first and fourthswitching elements TR1 and TR4. The two control pulse signals providedto the sixth and seventh switching elements TR6 and TR7 of the auxiliaryswitching circuit 14 rise together with the two control pulse signalsprovided to the second and third switching elements TR2 and TR3 and falla predetermined time t1 before the two control pulse signals areprovided to the second and third switching elements TR2 and TR3. Thatis, the fifth to eighth switching elements TR5 to TR8 are activatedsimultaneously with the corresponding first to fourth switching elementsTR1 to TR4 but are deactivated a predetermined time t1 before thecorresponding first to fourth switching elements TR1 to TR4 aredeactivated. The predetermined time t1 is set to a time allowing forsufficient discharging of the auxiliary capacitor C3. This allows forthe soft switching operation to be performed in which the switchingelements TR1 to TR4 are deactivated after sufficient discharging.

During the ON period of the fifth and eighth switching elements TR5 andTR8, the voltage across the terminals of the first smoothing capacitorC1, that is, half of the DC voltage obtained by converting the 400 Vseries AC voltage into DC voltage (voltage equal to the DC voltageconverted from the 200 V series AC voltage), is supplied to the invertercircuit 13. The voltage across the terminals of the auxiliary capacitorC3 is supplied to the inverter circuit 13 until the fifth and eighthswitching elements TR5 and TR8 are deactivated and the discharging ofthe auxiliary capacitor C3 at the downstream side is completed. In thesame manner, during the ON period of the sixth and seventh switchingelements TR6 and TR7, the voltage across the terminals of the secondsmoothing capacitor C2 (voltage equal to the voltage across theterminals of the first smoothing capacitor C1) is supplied to theinverter circuit 13. The voltage across the terminals of the auxiliarycapacitor C3 is supplied to the inverter circuit 13 until the sixth andseventh switching elements TR6 and TR7 are deactivated and thedischarging of the auxiliary capacitor C3 at the downstream side iscompleted. Thus, in the inverter circuit 13, the voltage across theterminals of the first smoothing capacitor C1 is mainly applied to theprimary side coil of the transformer INT during the ON period of thefirst and fourth switching elements TR1 and TR4. Further, the voltageacross the terminals of the second smoothing capacitor C2 is mainlyapplied in the opposite direction to the primary side coil of thetransformer INT during the ON period of the second and third switchingelements TR2 and TR3.

The first to fourth switching elements TR1 to TR4 are deactivated whenthe predetermined time t1 elapses, during which the auxiliary capacitorC3 is sufficiently discharged, after the corresponding fifth to eighthswitching elements TR5 to TR8 are deactivated and the supply of the DCvoltage from the DC converter circuit 12 is stopped. This reduces theswitching loss when the first to fourth switching elements TR1 to TR4are deactivated. The fifth to eighth switching elements TR5 to TR8 aredeactivated in a state in which the corresponding upstream smoothingcapacitors C1 and C2 and the downstream auxiliary capacitor C3 have thesame voltage across the terminals. This reduces the switching loss whenthe fifth to eighth switching elements TR5 to TR8 are deactivated.Further, due to the relationship of the leakage inductance and the likeat the primary side coil of the transformer INT, the switching loss isfurther reduced when the first to fourth switching elements TR1 to TR4and the fifth to eighth switching elements TR5 to TR8 are activated.

In the PWM control, the on pulse widths Wm and Ws of the control pulsesignal provide to the first to fourth switching elements TR1 to TR4 ofthe inverter circuit 13 and the fifth to eighth switching elements TR5to TR8 of the auxiliary switching circuit 14 are set to gradually narrowas the request changes from a large output to an intermediate output andfrom an intermediate output to a small output. The control of the firstto eighth switching elements TR1 to TR8 shifts from PWM control to PSMcontrol during the extremely small output request in which the on pulsewidth Wm is set to a width that is narrower than the minimum width Wm0.

The on pulse width Ws follows the on pulse width Wm. Thus, only the setwidth of the on pulse width Wm needs to be monitored. As will bedescribed later, the on pulse width Wm when a 200 V series AC power issupplied (hereinafter referred to as the 200 V series input) changes inthe same manner as a 400 V series input, and the on pulse width Wschanges greatly. Accordingly, the control can be switched with the samepulse width determination regardless of a 200 V series AC power or a 400V series AC power by monitoring the set width of the on pulse width Wm.

During an extremely small output request, the PSM control using thecontrol pulse signal as shown in FIG. 4 is performed. In the PSMcontrol, in a state in which the on pulse widths Wm and Ws of thecontrol pulse signal provided to the switching elements TR1 to TR8 ofthe inverter circuit 13 and the auxiliary switching circuit 14 are fixedat the minimum widths Wm0 and Ws0, phase adjustment is performed on thesame set of control pulse signals. In the present embodiment, the firstswitching element TR1 and the third switching element TR3 of theinverter circuit 13 are assigned as the reference phase, and the fourthswitching element TR4 and the second switching element TR2 are assignedas the control phase shifted to a phase retarded from the referencephase. The phases of the fifth to eighth switching elements TR5 to TR8in the auxiliary switching circuit 14 are not adjusted.

The phase (control phase) of the control pulse signal of the fourthswitching element TR4 and the second switching element TR2 is set tohave a phase difference α from the phase (reference phase) of thecontrol pulse signals of the first switching element TR1 and thirdswitching element TR3, which are of the same set. The phase difference αincreases as the output requested during the extremely small outputrequest decreases. That is, the ON period of the first and fourthswitching elements TR1 and TR4 and the ON period of the second and thirdswitching elements TR2 and TR3 of the same set greatly shift as therequesting output decreases and the voltage application time at theprimary side coil of the transformer INT at the downstream sideshortens. This ensures that each of the switching elements TR1 to TR8 isactivated when the output of the power supply device 11 is extremelysmall and solves the problems of output stability, biased magnetism, andthe like.

The phase (control phase) of the control signal of the fourth switchingelement TR4 and the second switching element TR2 is shifted to beretarded from the reference phase. Thus, the second and fourth switchingelements TR4 and TR2 are deactivated after the corresponding fifth toeighth switching elements TR5 to TR8 of the auxiliary switching circuit14 are deactivated. This maintains the effect of reducing the switchingloss of the fourth and second switching elements TR4 and TR2 of whichthe phases are changed by the PSM control.

Further, the PSM control shifts the phases of the control pulse signalshaving the on pulse widths Wm and Ws of the minimum widths Wm0 and Ws0at which the first to eighth switching elements TR1 to TR8 can besufficiently activated. The generation of unnecessary reflux current isreduced at the primary side of the transformer INT, and the power supplydevice 11 consumes less power.

During a 200 V series input, the switching switch S1 is deactivated.This disconnects the node N1 of the first and second smoothingcapacitors C1 and C2 from the node N2 of the seventh and eighthswitching elements TR7 and TR8. In this case, as shown by the timingwaveform charts of FIGS. 5 to 7, the output control circuit SC controlsthe first to fourth switching elements TR1 to TR4 of the invertercircuit 13 and the fifth and sixth switching elements TR5 and TR6 of theauxiliary switching circuit 14 with a plurality of control pulsesignals. During a 200 V series input, the seventh and eighth switchingelements TR7 and TR8 are maintained in the deactivated state.

Specifically, during a large to small output request, the output controlcircuit SC performs the PWM control using a plurality of control pulsesignals, as shown in FIG. 5 and FIG. 6. The operation of the invertercircuit 13 is similar to that during a 400 V series input. Each controlpulse signal provided to the first to fourth switching elements TR1 toTR4 is similar to that during a 400 V series input.

The seventh and eighth switching elements TR7 and TR8 of the auxiliaryswitching circuit 14 are maintained in the deactivated state. In thesame manner as a 400 V series input, the two control pulse signalsprovided to the fifth and sixth switching elements TR5 and TR6 fall apredetermined time t1 before when the control pulse signals of thecorresponding first to fourth switching elements TR1 to TR4 fall. Thetiming at which the two control pulse signals provided to the fifth andsixth switching elements TR5 and TR6 rise is changed. The timing atwhich the control pulse signal provided to the fifth switching elementTR5 rises is set to be the same as the timing at which the on pulseimmediately before the two control pulse signals provided to the secondand third switching elements TR2 and TR3 rise. The timing at which thecontrol pulse signal provided to the sixth switching element TR6 risesis set to be the same as the timing at which the on pulse immediatelybefore the two control pulse signals provided to the first and fourthswitching elements TR1 and TR4 rise.

The voltage at the two ends of the first and second smoothing capacitorsC1 and C2, that is, the DC voltage from the DC converter circuit 12, issupplied to the inverter circuit 13 when the fifth and sixth switchingelements TR5 and TR6 are both activated. That is, the same DC voltage issupplied to the inverter circuit 13 regardless of a 200 V series inputand a 400 V series input.

When performing soft switching control for deactivating the fifth andsixth switching elements TR5 and TR6 before the first to fourthswitching elements TR1 to TR4 of the inverter circuit 13, the switchingswitch S1 disconnects the node N1 of the first and second smoothingcapacitors C1 and C2 and the node N2 of the seventh and eighth switchingelements TR7 and TR8. This prevents the voltage at the node N1 of thefirst and second smoothing capacitors C1 and C2 from being supplied bythe two diodes D7 and D8 to the inverter circuit 13. This obtains theeffect of reducing the switching loss in the soft switching controlduring a 200 V series input.

In the PWM control during a 200 V series input, the on pulse widths Wmand Ws of each control pulse signal provided to the first to fourthswitching elements TR1 to TR4 of the inverter circuit 13 and the fifthto eighth switching elements TR5 to TR8 of the auxiliary switchingcircuit 14 are set to gradually narrow in accordance with changes in therequest from a large output to an intermediate output, and from anintermediate output to a small output. The control of the first toeighth switching elements TR1 to TR8 shifts from PWM control to PSMcontrol during an extremely small output request that sets the on pulsewidth Wm to a narrower width than the minimum width Wm0.

During a 200 V series input, the minimum width Ws0 of the on pulse widthWs of the control pulse signal provided to the auxiliary switchingcircuit 14 is sufficiently wide even if the on pulse width Wm of thecontrol pulse signal provided to the inverter circuit 13 is the minimumwidth Wm0.

During an extremely small output request, the PSM control using thecontrol pulse signal as shown in FIG. 7 is performed. PSM control duringa 200 V series input is an operation similar to that during a 400 Vseries input. The phase (control phase) of the control pulse signalprovided to the fourth switching element TR4 and the second switchingelement TR2 of the control phase is shifted to be retarded from thereference phase. This further shortens the voltage application time ofthe primary side coil in the downstream transformer INT. As describedabove, the on pulse width Ws of the control pulse signal provided to theauxiliary switching circuit 14 is set to be narrower than a 400 V seriesinput. The on pulse width Ws of the control pulse signal provided to theauxiliary switching circuit 14 is set to be sufficiently wide during a200 V series input. This ensures that each switching element TR1 to TR8is activated even when the output of the power supply device 11 isextremely small.

The present embodiment has the advantages described below.

(1) The power supply device 11 is applicable to any one of the inputpower supplies of a 200 V series (first voltage value) and a 400 Vseries (second voltage value) due to the switching of the operation ofthe auxiliary switching circuit 14 based on the switching of theswitching switch S1. When a large output is requested, PWM control isperformed to adjust the on pulse widths Wm and Ws of the control pulsesignals provided to the first to eighth switching elements TR1 to TR8 ofthe inverter circuit 13 and the auxiliary switching circuit 14, whichoperates in cooperation with the inverter circuit 13. When a smalloutput is requested, PSM control is performed to adjust the phasedifference α of two control pulse signals provided to the first tofourth switching elements TR1 to TR4 in the same set of the invertercircuit 13. In this manner, when performing PWM control during a lowoutput request, each switching element TR1 to TR8 of the invertercircuit 13 and the auxiliary switching circuit 14 may not be activated.Thus, PSM control is performed during a low output request, and theoutput is lowered by the phase adjustment in a state in which the onpulse widths Wm and Ws of each control pulse signal are ensured. In thepresent embodiment, this is performed in a state in which the on pulsewidths Wm and Ws of each control pulse signal is fixed to the minimumwidths Wm0 and Ws0 allowing for activation. Activation of each of theswitching elements TR1 to TR8 of the inverter circuit 13 and theauxiliary switching circuit 14 is ensured even when there is a lowoutput request for any of the input power supplies of the 200 V seriesand the 400 V series. Thus, a stable output can be obtained.

(2) When the on pulse widths Wm and Ws are the minimum widths Wm0 andWs0, the control of the first to eighth switching elements TR1 to TR8switches from PWM control to PSM control. During PSM control, the phaseof each control pulse signal is adjusted in a state fixed at the minimumwidths Wm0 and Ws0 that sufficiently activates the first to eighthswitching elements TR1 to TR8. Thus, when switching to PSM control, theminimum widths Wm0 and Ws0 are maintained, and activation of each of theswitching elements TR1 to TR8 in the inverter circuit 13 and theauxiliary switching circuit 14 is ensured. This stabilizes the output aswell as the output when switching controls.

(3) The deactivation of the fifth to eighth switching elements TR5 toTR8 in the auxiliary switching circuit 14 before the first to fourthswitching elements TR1 to TR4 of the inverter circuit 13 are deactivatedis maintained even when the phase adjustment of the control pulse signalis performed during PSM control. Thus, the soft switching operation inwhich the first to fourth switching elements TR1 to TR4 of the circuit13 are deactivated after the voltage supply to the inverter circuit 13is stopped is maintained even during PSM control. This reduces switchingloss even during PSM control.

(4) The control of the output control circuit SC switches the switchingswitch S1 to a connecting state based on the determination of a 400 Vseries input and switches the switching switch S1 to a disconnectingstate based on the determination of a 200 V series input. In thismanner, the switching of the switching switch S1 is automaticallyperformed under the control of the output control circuit SC1. Thus,there is no need for a manual operation.

(5) During PSM control, when the period (period in which only theswitching elements TR4 and TR2 are activated) from when the switchingelements TR1 and TR3 are deactivated to when the switching elements TR4and TR2 are deactivated becomes long, unnecessary reflux current isgenerated at the primary side coil. In the present embodiment, however,the on pulse widths Wm of the switching elements TR4 and TR2 during PSMcontrol is set to the minimum width Wm0. This prevents the generation ofunnecessary reflux current. Further, the reduction in conduction lossduring reflux current generation lowers power consumption. In the arcmachining power supply device 11 of the present embodiment, a largeoutput current may be generated during a low output. This may lengthenthe time during which the reflux current is generated. The presentembodiment can effectively reduce the reflux current. This has greatsignificance when embodied in the arc machining power supply device 11.

It should be apparent to those skilled in the art that the presentinvention may be embodied in many other specific forms without departingfrom the spirit or scope of the invention. Particularly, it should beunderstood that the present invention may be embodied in the followingforms.

In the embodiment described above, the same control pulse signal isprovided to the first to fourth switching elements TR1 to TR4 in thesame set. However, one of the two control pulse signals in the same setmay always be set to the maximum width Wmx. As shown by the waveformtaken during PSM control for a 400 V series input in FIG. 8 and thewaveform taken during PSM control for a 200 V series input in FIG. 9,for example, the on pulse width Wm of the control pulse signal of thefirst and third switching elements TR1 and TR3 having the referencephase is always fixed at the maximum width Wmx during the PSM controland during PWM control (not shown). In contrast, as for the controlpulse signal of the fourth and second switching elements TR4 and TR2having the control phase, the on pulse width Wm may be changed duringPWM control and the phase may be retarded (phase difference α) duringPSM control. In this case, the deactivation of the switching elementsTR5 to TR8 before deactivation of the switching elements TR1 to TR4 ismaintained. This maintains the soft switching operation. The phase mayalso be advanced. The switching elements TR1 to TR4 of the control phaseand the reference phase may be exchanged.

In the embodiment described above, one of the first to fourth switchingelements TR1 to TR4 in the same set of the inverter circuit 13 is set asthe subject (control phase) for phase shifting during PSM control.However, the fifth to eight switching elements TR5 to TR8, for example,the fifth and sixth switching elements TR5 and TR6 of the auxiliaryswitching circuit 14 may be set as the subject for phase shifting. Asshown by the waveform taken during PSM control for a 400 V series inputin FIG. 10 and the waveform taken during PSM control for a 200 V seriesinput in FIG. 11, for example, the control pulse signal of the first tofourth switching elements TR1 to TR4 may be fixed and the phase may beadvanced (phase difference α) from the control pulse signal of the fifthand sixth switching elements TR5 and TR6. This also maintains thedeactivation of the fifth to eighth switching elements TR5 to TR8 beforethe deactivation of the first to fourth switching elements TR1 to TR4.Thus, the soft switching operation is maintained. Only the waveformtaken during PSM control for a 200 V series input is shown in FIG. 12.However, the phase of the control pulse signal of the fifth and sixthswitching elements TR5 and TR6 may be retarded. The phase of the seventhand eighth switching elements TR7 and TR8 may be shifted during a 400 Vseries input. The fifth to eighth switching elements TR5 to TR8 may allbe set as the subject for phase shifting.

The subject (control phase) of phase shifting during PSM control is oneof the first to fourth switching elements TR1 to TR4 in the same set ofthe inverter circuit 13. However, the first to fourth switching elementsTR1 to TR4 may all be set as the subject for phase shifting. As shown bythe waveform taken during PSM control for a 400 V series input in FIG.13 and the waveform taken during PSM control for a 200 V series input inFIG. 14, for example, the phase may be retarded (phase difference α)from the control pulse signal of the switching elements TR1 to TR4. Thisalso maintains the deactivation of the fifth to eighth switchingelements TR5 to TR8 before the deactivation of the first to fourthswitching elements TR1 to TR4. This maintains the soft switchingoperation. Only a waveform taken during PSM control for a 200 V seriesinput is shown in FIG. 15. However, the phase of the control pulsesignal of the first to fourth switching elements TR1 to TR4 may beadvanced. The phase of either the seventh and eighth switching elementsTR7 and TR8 or the fifth and sixth switching elements TR5 and TR6 may beshifted in synchronism with the first to fourth switching elements TR1to TR4 during a 400 V series input.

Furthermore, the modes of the PWM control and the PSM control of theinverter circuit 13 and the auxiliary switching circuit 14 may becombined with various modes described above. Further, in addition tobeing determined in advance as the specification, the mode of controlmay also be changed during control.

In the embodiment described above, the predetermined narrow pulse widthused for determining switching determination from PWM control to PSMcontrol is set to the minimum width Wm0 and Ws0 but may be set to awidth slightly larger than the minimum width Wm0 and Ws0 at which theswitching elements TR1 to tR8 can be activated. The control may beswitched based on, for example, the actual output value or the setoutput value of the power supply device 11 in addition to the pulsewidth.

The configuration of the power supply device 11 in the embodimentdescribed above may be changed. For example, the switching elements TR1to TR8 are formed by IGBTs but may be formed by switching elements otherthan IGBTs such as MOS transistors, thyristors, and the like.

The switching switch S1 includes a relay. However, a switch other than arelay such as a semiconductor switch may be used. The switch isautomatically switched in the present embodiment. A switch that ismanually switched may be used instead.

The output converter circuit is formed by the rectifier circuit DR2 andthe DC reactor DCL but may be changed in accordance with the load.

The DC converter circuit 12 is used for a specification that inputs ACpower. However, the DC converter circuit 12 may be omitted or bereplaced by a voltage converter circuit or the like for a specificationthat inputs DC power.

The power supply device 11 of the embodiment described above is an arcmachining power supply device. However, the power supply device 11 maybe applied to other power supply devices.

A technical idea, which can be grasped from the above embodiments andother cases, is described below.

A power supply device comprising:

-   -   an inverter circuit including a bridge circuit of first to        fourth switching elements, wherein predetermined sets of the        first to fourth switching elements are alternately activated and        deactivated to convert DC voltage supplied by two power lines        into a predetermined AC voltage;    -   an auxiliary switching circuit including        -   an auxiliary capacitor connected between the two power lines            at a downstream side of the inverter circuit,        -   first and second smoothing capacitors connected in series            between the two power lines at a downstream side of the            auxiliary capacitor,        -   fifth and sixth switching elements respectively arranged on            the two power lines between the first and second smoothing            capacitors and the auxiliary capacitor,        -   seventh and eighth switching elements connected in series            between the two power lines between the first and second            smoothing capacitors and the auxiliary capacitor, and        -   a switching unit that connects or disconnects a first node            of the first and second smoothing capacitors and a second            node of the seventh and eighth switching elements, wherein            -   the switching unit disconnects the first and second                nodes when the input AC power has a first voltage value                to supply a voltage across two terminals of the first                and second smoothing capacitors to the inverter circuit,                and            -   the switching unit connects the first and second nodes                when the input AC power has a second voltage value that                is two times greater than the first voltage value so                that soft switching control is performed by activating                and deactivating predetermined sets of the fifth to                eighth switching elements, alternately supplying the                inverter circuit with a voltage across the terminals of                the first or second smoothing capacitor, and        -   deactivating a predetermined one of the fifth to eighth            switching elements before the first to fourth switching            elements are deactivated to stop the voltage supplied to the            inverter circuit;    -   a pulse width modulation control unit that adjusts an on pulse        width of a control pulse signal provided to the first to fourth        switching elements and adjusts an on pulse width of a control        pulse signal provided to the fifth to eighth switching elements        accordance with the adjusted width;    -   a phase shift control unit that adjusts a phase difference of        two control pulse signals provided to the same set of switching        elements in the first to fourth switching elements or adjusts a        phase difference of two control pulse signals provided to        predetermined ones of the first to fourth switching elements and        corresponding ones of the fifth to eighth switching elements;        and    -   two control pulse signals provided to the switching elements in        a same set of the first to fourth switching elements, or for        adjusting a mutual phase difference of a pair of control pulse        signals provided to a predetermined switching element of the        first to fourth switching elements and a corresponding switching        element of the fifth to eighth switching elements; and    -   a control switching unit that operates the pulse width        modulation control unit when a relatively large output is        requested and operates the phase shift control unit when a        relatively small output is requested.

The invention claimed is:
 1. A power supply device comprising: a DCconverter circuit including a rectifier circuit and first and secondsmoothing capacitors, which are connected in series and arranged betweentwo power lines at an output side of the rectifier circuit, wherein theDC converter circuit rectifies and smooths input AC power and convertsthe input AC power into DC voltage; an inverter circuit including abridge circuit of first to fourth switching elements, whereinpredetermined sets of the first to fourth switching elements arealternately activated and deactivated to convert the DC voltage to apredetermined AC voltage; an auxiliary switching circuit including anauxiliary capacitor, which is connected between the two power linesbetween the DC converter circuit and the inverter circuit, fifth andsixth switching elements respectively arranged on the two power linesbetween the DC converter circuit and the auxiliary capacitor, seventhand eighth switching elements connected in series between the two powerlines between the auxiliary capacitor and the first and sixth switchingelements, and a switching unit that connects or disconnects a first nodeof the first and second smoothing capacitors and a second node of theseventh and eighth switching elements, wherein the switching unitdisconnects the first and second nodes when the input AC power has afirst voltage value to supply a voltage across two terminals of thefirst and second smoothing capacitors to the inverter circuit, and theswitching unit connects the first and second nodes when the input ACpower has a second voltage value that is two times greater than thefirst voltage value so that soft switching control is performed byactivating and deactivating predetermined sets of the fifth to eighthswitching elements, alternately supplying the inverter circuit with avoltage across the terminals of the first or second smoothing capacitor,and deactivating a predetermined one of the fifth to eighth switchingelements before the first to fourth switching elements are deactivatedto stop the voltage supplied to the inverter circuit; a pulse widthmodulation control unit that adjusts an on pulse width of a controlpulse signal provided to the first to fourth switching elements andadjusts an on pulse width of a control pulse signal provided to thefifth to eighth switching elements in accordance with the adjustedwidth; a phase shift control unit that adjusts a phase difference of twocontrol pulse signals provided to the same set of switching elements inthe first to fourth switching elements or adjusts a phase difference oftwo control pulse signals provided to predetermined ones of the first tofourth switching elements and corresponding ones of the fifth to eighthswitching elements; and a control switching unit that operates the pulsewidth modulation control unit when a relatively large output isrequested and operates the phase shift control unit when a relativelysmall output is requested, wherein the control switching unit operatesthe phase shift control unit when an output is requested that may resultin the on pulse width being smaller than the predetermined narrow pulsewidth to adjust a phase of the control pulse signal in a state in whichthe on pulse width of the control pulse signal provided to the first tofourth switching elements is fixed at a first narrow pulse width and theon pulse width of the control pulse signal provided to the fifth toeighth switching elements is fixed at a second narrow pulse width. 2.The power supply device according to claim 1, wherein the controlswitching unit operates the pulse width modulation control unit when anoutput is requested that sets the on pulse width to be larger than apredetermined narrow pulse width allowing for each of the switchingelements to be sufficiently activated.
 3. The power supply deviceaccording to claim 1, wherein the phase shift control unit adjusts thephase of the control pulse signal provided to the first to eighthswitching elements so that the fifth to eighth switching elements aredeactivated before the first to fourth switching elements aredeactivated.
 4. The power supply device according to claim 1, furthercomprising a switch control unit that controls the switching unit toconnect the first and second nodes when the input AC power has thesecond voltage value and disconnects the first and second nodes when theinput AC power has the first voltage value.
 5. An arc machining powersupply device comprising: the power supply device according to claim 1;and a rectifier circuit that rectifies the predetermined AC voltageprovided from the power supply device and generates an arc machiningvoltage for performing arc machining on a machining subject.